Illuminating devices for operating microscopes generally use an illuminating beam path which is at an angle in the region of about 6° to the observation beam path (so-called 6° illumination). This avoids the undesirable shadowing which would occur at larger angles between the observation beam path and the illuminating beam path.
Eye surgery places additional special demands on the illumination of a microscope. To start with, a sufficiently plastic image is obtained at an illuminating angle of, again, about 6°. However, for certain ophthalmic observations or interventions it is necessary to produce the so-called red reflex. In this, the pupil of the eye being operated on shines reddish as a result of the light refracted by the retina. This method of illumination is of great importance in cataract operations, for example, as tissue residues show up particularly well in the counter-light of the red reflex. The production of the red reflex requires smaller angles between the observation beam path and the illuminating beam path, the angles preferably being in the range from 0° to 2° (so-called 0° or 2° illumination).
Operating microscopes which are configured with two pairs of stereoscopic observation beam paths for a first observer (main surgeon) and a second observer (assistant), respectively, often have the disadvantage that the red reflex is very easy for the main surgeon to see but cannot be seen satisfactorily by the co-observer. The latter will only see a good red reflex in one of his two observation channels, depending on his position, either to the right or left of the main surgeon. This has an adverse effect on stereoscopic viewing.
DE 040 28 605 discloses an illuminating device for an operating microscope with an illuminating system that is arranged outside the optical axis of the microscope objective and illuminates the operating area parallel to the axis of the objective through the microscope objective, and a deflector element on the side of the microscope objective remote from the object, which illuminates the operating area with a fraction of the illuminating light along the axis of the objective. This illuminating device is characterised in that the illuminating system is equipped, on the objective side, with a reflecting element which reflects the illuminating light parallel to the objective axis towards the microscope objective, and in that the deflector element illuminates the operating area at an angle of inclination relative to the objective axis that is smaller than the angle of inclination at which the reflecting element illuminates the operating area. The larger angle of inclination is preferably 6°, the smaller angle is variable from 0° to 6°. The illuminating device described in this publication does not contain any solution for providing, for example, a red reflex for a second observer (assistant).
DE 103 11 000 B4 discloses an illuminating device for a microscope having at least one observation beam path, particularly an operating microscope, with an illuminating system and a deflector device for deflecting light emanating from a light source onto an object that is to be observed, e.g. an eye that is to be operated on, the deflector device providing illumination of the object at different illuminating angles with respect to the at least one observation beam, and the deflector device comprising two deflector elements that are at least partly configured as physical beam splitters. This illuminating device uses three deflector elements to provide a 6° and a 2° illumination for a main surgeon and an assistant.
An illuminating device is known from DE 102 08 594 in which, in one embodiment, two parallel illuminating beam pencils are used. These are deflected from deflector elements with a total mirror finish. Because of the total mirror finish these deflector elements cannot be placed in the observation beam paths, which means that certain minimum angles between the optical axis of a main objective or the observation beam paths and the illuminating beam paths are unavoidable. However, to provide the optimum red reflex, the angles should be as small as possible.